To determine single-piece weight in any mailing of nonidentical-weight pieces, weigh each piece individually. To determine single-piece weight in a mailing of identical-weight pieces, weigh a sample group of at least 10 randomly selected pieces and divide the total sample weight by the number of pieces in the sample. Express all single-piece weights in decimal pounds rounded off to four decimal places.

Parcel Post mail is not sealed against postal inspection. Regardless of physical closure, the mailing of articles at Parcel Post prices constitutes consent by the mailer to postal inspection of the contents.

Parcel Post mail consists of mailable matter that is neither mailed or required to be mailed as First-Class Mail nor entered as Periodicals (except as permitted under 3.2 or permitted or required under 707.7.9). The general public (other than publishers or registered news agents) may mail copies of Periodicals publications at Parcel Post prices.

Incidental First-Class Mail matter may be enclosed in or attached to any Parcel Post piece without payment of First-Class Mail postage. An incidental First-Class Mail attachment or enclosure must be matter that, if mailed separately, would require First-Class Mail postage, is closely associated with but secondary to the host piece, and is prepared so as not to interfere with postal processing. An incidental First-Class Mail attachment or enclosure may be a bill for the product or publication, a statement of account for past products or publications, or a personal message or greeting included with a product, publication, or parcel. Postage at the Parcel Post price for the host piece is based on the combined weight of the host piece and the incidental First-Class Mail attachment or enclosure.